Dynamoelectric machine and method for manufacturing same

ABSTRACT

A dynamoelectric machine constructed for speed and accuracy of manufacturing has a stator core constructed of 90° symmetrical stator laminations and the windings have differing numbers of poles which overlap in slots of the stator core are wound of the core formed by the laminations in unique fashion. The rotor bars of the machine are skewed to optimize performance of the machine when in the form of a single phase induction motor. Magnet wire leads of the windings are connected directly to terminals on a plug and terminal assembly which is formed for positive location on an end frame of the machine without welding or other fastening to the end frame. The end frames of the machine and stator laminations forming the stator core are formed so as to increase the precision of the final position of the stator relative to the rotor assembly of the dynamoelectric machine. The end frames are constructed for grounding without the use of fasteners or wire. The engagement of the end frames with the stator core is employed as the basis for alignment of the machine components.

This is a continuation of application Ser. No. 08/139,578, filed Oct.20, 1997.

FIELD OF THE INVENTION

This invention relates generally to electrical apparatus and inparticular to a dynamoelectric machine and a method of manufacturing thedynamoelectric machine.

BACKGROUND OF THE INVENTION

Competitive mass production of dynamoelectric machines in the form ofelectric motors such as those used in household appliances and othermachines requires in the design and manufacture of the motor asimultaneous emphasis on speed and simplicity of manufacture, and theprecision of the final motor construction. Moreover, any design ormanufacturing process must not add costs out of proportion to thesavings achieved through higher production. Thus, the present inventionpertains to a motor which incorporates design features optimized forspeed of manufacture and precision of the final product.

It is well established that the formation of the stator core of anelectric motor may be most efficiently carried out by forming the corefrom a stack of laminations stamped from a sheet of highly magneticallypermeable material. The laminations are frequently square because thisshape wastes less of the sheet material from which the laminations arestamped. Each lamination is stamped with a central opening and radiallyextending slots which typically open into the central opening. Thecentral openings of the stator laminations in the stack form the bore ofthe stator core and the slots define the teeth which extend the lengthof the stator bore and receive the wire windings of the motor. The slotsare stamped symmetrically about the center of the central opening,leaving substantially equal amounts of material along each of the fouredges of the lamination. Thus, the amount of magnetic flux which can becarried by the stator core is substantially the same along all four ofits sides.

It is important that the stator bore be round and straight so that therotor may freely rotate in the stator core bore while maintaining only aminimal separation between the rotor and the stator core. Thestraightness of the bore is adversely affected by the inherent presenceof variations in thickness (called "gamma" variation) of the rolledsheet material from which the laminations are stamped, so that eachlamination is not truly flat. If the laminations are stacked one on topof the other in the same orientation as when each lamination was stampedon the sheet material, the gamma variations will tend to add togetherrather than cancel out. Thus, the stator bore formed may besubstantially curved and unsuitable for mating with the rotor in such away which will permit the rotor to freely rotate in the stator bore.Punching the central openings of the laminations from the sheet materialrelieves certain stresses in the material, which tends to cause thematerial to elastically deform from the round shape struck by the punch,to an elliptical shape. Further deviations from round may be introducedby thermal stress as the stator core is annealed. Again, if thelaminations are stacked together in such a way as to add the deviationsfrom round, a bore which is too elliptical to receive the rotor may beproduced. In a square lamination having substantially equal amounts ofmaterial remaining after punching on all four sides, deformationscausing deviation from round can be expected to occur approximatelyequally along two perpendicular axes lying in the plane of thelamination. Accordingly, it is preferred to rotate each lamination 90°relative to the adjacent lamination in the stack so that gammavariations and deviations from round in the laminations tend to canceleach other out.

However, in the past 90° rotation of each lamination relative to theadjacent lamination in the stack has not been practical whenconstructing stator cores for certain two speed electric motors havingtwo windings which have different numbers of poles. In a two speed motorhaving a four pole winding and a six pole winding, some of the turns ofwire forming the poles must be placed in the same stator slots. In orderto provide enough room, the slots where the windings will overlap mustbe deeper. This requirement introduces asymmetry in the arrangement ofslots about the center of the central opening of each lamination, andreduces the amount of material on two of the sides of the laminationrelative to the other sides. Equalizing the amount of material on allfour sides may be accomplished by elongating the two sides having thedeepest slots. However, the combination of the asymmetry of the slotarrangement and the rectangular shape of the lamination makes itimpossible to rotate the laminations 90° relative to the adjacentlamination when stacking. The best that can be done presently is torotate the laminations 180°, which does not permit cancellation ofmanufacturing tolerances as efficiently as 90° rotation, and thusadversely affects the roundness and straightness of the bore.

It is well known that in order to decouple stator slot order harmonicsthe rotor bars in the squirrel cage rotor of an induction motor shouldbe skewed. Typically, skewing is accomplished by turning the rotorlaminations making up the rotor slightly with respect to each other sothat the passages formed by overlapping slots of the rotor laminationsare generally helical in shape. Helical skewing can be carried out byhand using a jig, or automatically by machine. In the former instance,substantial labor costs are added to the production of the rotor, and inthe latter instance it is difficult to reliably automate the delicateoperation of turning the rotor laminations slightly relative to eachother. Further, the helical passages have a stair-step configurationwhich can produce undesirable turbulence in the molten material pouredinto the passages to form the rotor bars. Significant savings can berealized by implementation of a "straight" skew, in which the rotor barpassage consists of two smooth, straight passages which overlap, but areskewed. The skewed passage is typically formed by making the rotor slotsasymmetrical about a radial line of the rotor lamination, with the slotsin one half of the stack of laminations forming the rotor being themirror image of the slots in the other half. Although decoupling slotharmonics by using two straight passages which are skewed relative toone another is known, there is presently a need for such a straight skewwhich delivers better motor performance for single phase motors.

Once the rotor and stator have been constructed, it is necessary toassure that the rotor will be aligned with the stator core bore when therotor is inserted into the bore. The rotor shaft is typically supportedfor free rotation at its ends in central openings in metal end frameswhich are connected to the stator core. Tolerances inherent in theformation of the central openings in the end frames and the stator corebore, and the absence of accurate location mechanism for the end frameson the stator core result in many rotor/stator core assemblies being outof alignment. Present practice calls for the introduction of shims inthe central openings where the rotor shaft is received to bring therotor and stator core into alignment. This procedure permits only arelatively coarse adjustment, and requires time and extra labor toaccomplish.

The manufacturing step of mounting the rotor shaft on the end framesalso presently requires significant labor and time to accomplish. Theends of the rotor shaft are mounted by bearings in the central openingsof the end frames which permit free rotation of the rotor shaft aboutits longitudinal axis. Presently, the bearings include many parts andrequire substantial time to assemble and install in the end frames.

The inner raceways of the bearings held in the central openings of theend frames are typically fixed to the rotor shaft at predeterminedlocations. Thus, the relative location of the end frames is determinedby the predetermined locations on the rotor shaft. The presence oftolerances in the dimensions of the rotor shaft, the end frames and thestator core occasionally results in the stator core and end frames notfitting together as they should in the assembly of the machine. A minormisalignment or structural irregularity of the rotor shaft may cause theshaft to wobble as it rotates. The wobble causes variations in the airgap (i.e., the distance separating the rotor and the stator core) whichresults in undesirable noise and vibration.

Another aspect of the assembly of the electric motor which is laborintensive is the electrical connection of the windings to a plug andterminal assembly used to connect the windings to a source ofelectricity and to control operation windings for starting the machine.Presently, there are at least four connections used to electricallyconnect the terminal end of each magnet wire to the plug and terminalassembly. The magnet wire is first connected to a terminal having sharpridges which pierce the insulation on the wires to make electricalcontact as the terminals are crimped against the magnet wire. The ridgedterminal is connected to wire having plastic insulation, which is inturn connected to a terminal on the plug and terminal assembly. Theterminal on the plug and terminal assembly is connected to the circuitryin the plug and terminal assembly. Typically, only two of theseconnections are made during assembly of the motor. However, eachterminal connection is a more likely site for failure. Moreover,connection of the plug and terminal assembly to the end frames of themotor presently requires separate fasteners. The use of such fasteners,or alternative joining methods such as welding or soldering, adds thecost of the fasteners or joining material, and the cost of labor toconnect the plug and terminal assembly by application of the fastenersor joining material.

In order to ground the motor end frames, a separate assembly step isrequired for ground connection. For instance, a screw may be receivedthrough an end frame and into the plug and terminal assembly, or theconnection may be by insulated wire. The insulated wire is connected tothe end frame by a screw or a clip, which are additional materials whichrequire additional time to manipulate during assembly of the motor.

SUMMARY OF THE INVENTION

Among the several objects and features of the present invention may benoted the provision of a dynamoelectric machine capable of rapidproduction while maintaining quality at or above that of existingmachines of the same type; the provision of such a machine which hasfewer parts; the provision of such a machine which is secured togetherwith fewer fasteners; the provision of such a machine which makes aneconomic use of materials in its construction; the provision of such amachine which has fewer internal electrical connections; the provisionof such a machine which is grounded without requiring additional wiringor special ground connections; the provision of such a machine which isautomatically connected to a ground remote from the machine whenconnected to a source of electrical power; the provision of such amachine in which the rotor and stator are accurately aligned; theprovision of such a machine which accommodates misalignment orstructural irregularity of the rotor without introducing substantialstresses to the machine during operation; and the provision of such amachine in which stator slot order harmonics are optimally decoupled.

Further among the objects and features of the present invention may benoted the provision of a method for manufacturing a dynamoelectricmachine which requires fewer steps to secure the component partstogether; the provision of such a method in which critical dimensionsare held within closer tolerances to produce more accurate alignment ofthe stator and rotor; the provision of such a method which employs fewerindividual fasteners; and the provision of such a method which can becarried out rapidly and at reasonable cost.

Generally, a two-speed dynamoelectric machine constructed according tothe principles of the present invention comprises a stator, at least twowindings on the stator, a rotor received in the stator and meanssupporting the rotor for rotation relative to the stator. A first of thetwo windings has a first number of poles and a second of the twowindings has a second number of poles different from the first number ofpoles. A plurality of stator laminations stacked one on top of the otherform the stator core. Each stator lamination comprises a sheet of highlymagnetically permeable material having a generally central openingtherein, and slots opening into the central opening and extendinggenerally radially outwardly therefrom. The slots are disposed in anarrangement around the periphery of the central opening and receiveturns of wire from the two windings of the dynamoelectric machine withat least some of the slots receiving turns of wire from both of the twowindings. The arrangement of slots on each stator lamination issymmetrical about a pair of perpendicular lines lying generally in theplane of the stator lamination and intersecting generally at the centerof the central opening, and about a diagonal line lying in the plane ofthe stator lamination, passing through the center of the central openingand making an angle of 45° with the perpendicular lines. Each statorlamination in the stack is rotated 90° relative to other statorlaminations about a longitudinal axis of a central rotor-receiving boreof the stator core formed by the central openings of the statorlaminations in the stack thereby forming a central bore which isstraighter and more nearly cylindrical.

In another aspect of the present invention, a dynamoelectric machinecomprises a stator including a stator core having a pair of opposing endfaces, a bore through the stator core extending from one end face to theother end face, and windings including a start winding and at least onerun winding on the stator, each winding having winding leads extendingoutwardly from the stator. First and second opposite end frames mountedon respective end faces of the stator core each have a generally centralopening. A rotor assembly comprises a shaft received in bearing meansassociated with the central openings of the end frames, and a rotorfixedly mounted on the shaft for conjoint rotation therewith. The rotoris disposed at least in part in the stator core bore, and the rotor andthe stator are adapted for magnetic coupling upon activation of thewindings for rotating the shaft and rotor relative to the stator and endframes. A plug and terminal assembly includes a casing made of aninsulator material, a plurality of lead terminals electrically connectedto the winding leads and a plurality of electrical connectors protrudingfrom the casing and electrically connected to the lead terminals. Theelectrical connectors are constructed for connecting the winding leadsto a source of electrical power. A ground tab mounted on and inelectrical contact with the second end frame is received in an openingin the casing with the ground tab being disposed for electricalconnection to ground upon connection of the electrical connectors toground.

In yet another aspect of the present invention, a dynamoelectric machinehas a stator, windings, end frames, bearing means and a rotor assemblyas described in the preceding paragraph. The dynamoelectric machinefurther comprises a plug and terminal assembly including a casing madeof insulator material. A switch housed in the casing is operable betweena first switch mode in which the start winding is activated and a secondswitch mode in which the start winding is deactivated. A plurality ofelectrical connectors are connected to the switch and adapted forconnection to a power supply, and a plurality of magnet wire terminalsare integrally connected to the switch and receive the terminal ends ofthe windings thereby providing direct connection of the windings to theswitch.

In still another aspect of the present invention, a dynamoelectricmachine comprises a stator, a rotor assembly, first and second endframes and first and second bearings. The first bearing is disposed in acentral opening of the first end frame and fixedly mounted on a rotorshaft of the rotor assembly thereby to prevent axial movement of therotor shaft relative to the first bearing. The second bearing, disposedin a central opening of the second end frame, comprises a housing andshaft bearing means supported by the housing in a shaft receivingpassage. The shaft bearing means is constructed and arranged for rollingengagement with the rotor shaft in the shaft receiving passage forsupporting the rotor shaft and permitting rotation of the rotor shaftabout its longitudinal axis. The shaft bearing means is free ofconnection to the rotor shaft.

Methods of manufacturing a dynamoelectric machine are also disclosed. Inone aspect of the method, end frames are each formed by simultaneouslypunching from sheet metal blank a generally central rotor shaftreceiving opening and locator means spaced from the center of thecentral opening so as to precisely locate the center of the centralopening relative to the locator means.

Other objects and features of the present invention will be in partapparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective of an electric motor;

FIG. 2 is a longitudinal section of the motor;

FIG. 3 is an exploded front perspective of the motor;

FIG. 4 is a perspective of the rear end frame of the motor, with a plugand terminal assembly illustrated as exploded away from the end frame;

FIG. 5 is an enlarged fragmentary perspective of the rear end frameshowing the plug and terminal assembly as installed on the end frame;

FIG. 6 is an enlarged fragmentary section taken in the plane includingline 6--6 of FIG. 5;

FIG. 7 is a front elevation of the plug and terminal assembly showinglocating posts of the assembly as received in a stator slot (shown inphantom);

FIG. 8 is an end elevation of the plug and terminal assembly and afragmentary portion of the stator core illustrating engagement of thelocating posts therewith;

FIG. 9 is a an electrical schematic of the plug and terminal assembly,shown as plugged into a power source;

FIG. 10 is an enlarged fragmentary cross section of the motorillustrating the locator nubs of the end frames and locator openings ofthe stator core;

FIG. 11 is a section of the rear end frame taken in the plane includingline 11--11 of FIG. 4 and showing a rotor shaft bearing mounted in thecentral opening of the rear end frame;

FIG. 12 is a longitudinal section of the rotor shaft bearing of FIG. 11;

FIG. 13 is an end elevation of a housing piece of the housing of therotor shaft bearing;

FIG. 14 is a fragmentary elevation of the opposite end of the housingpiece of FIG. 13; and

FIG. 15 is a plan of a stator lamination which forms the stator core;

FIG. 16 is a schematic illustrating the formation of stator laminationsand the stator core;

FIG. 17 is a perspective of a rotor assembly of the motor, including arotor shaft and a rotor core, with parts of the rotor core broken awayto show details of construction;

FIG. 18 is a plan view of the rotor core with portions broken away totwo levels to reveal the three different rotor slot orientations withinthe rotor core;

FIG. 19 is an enlarged fragmentary elevation of the rotor core showing asingle rotor slot and illustrating in hidden lines the orientation of anunderlying slot;

FIG. 20 is an enlarged fragmentary view of a rotor core having slotswhich are skewed accordingly to conventional mathematical prediction;and

FIG. 21 is a diagram illustrating two preferred windings of the motorand two other windings.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, and in particular to FIGS. 1, 3 and 15, adynamoelectric machine in the form of a single phase, two speedinduction motor 20 is shown to include a stator 22 having a core 24 madeup of a stack of thin stator laminations 26, and windings 27 on thestator core including a four pole start winding 28, a four pole runwinding 30 and a six pole run winding 32. The stator 20, stator core 24,stator laminations 26 and windings 27 are indicated generally by theirrespective reference numerals. The windings illustrated are exemplaryonly, as the invention is applicable to dynamoelectric machines of otherwinding configurations. A rotor assembly indicated generally at 36includes a rotor 38 received in a bore 40 of the stator core 24 and arotor shaft 42 fixedly connected to the rotor. Opposite end portions ofthe rotor shaft 42 are received in a first bearing 44 and a secondbearing (generally indicated at 46), respectively, for free rotation ofthe rotor assembly 36 about the longitudinal axis of the rotor shaft. Asmay be seen in FIG. 2, the first and second bearings 44, 46 are held incentral openings 48 of first and second end frames (designated generallyby reference numbers 50 and 52, respectively) which support the rotorassembly 36. A plug and terminal assembly, generally indicated at 56 islocated on the second end frame 52, and a centrifugal mechanism 58 ofthe type well known in the art is mounted on the rotor shaft 42 adjacentthe second end frame. The end frames 50, 52 engage opposite end faces ofthe stator core 24 where they are positively located by locator nubs 60associated with each end frame, which locator nubs are received incorresponding locator holes 62 in the end faces. The motor 20 is heldtogether by keys 64 which are received in preformed channels 66 in thestator core 24 and bent over at their ends 68 (shown in phantom in FIG.3) to hold the motor components together as shown in FIG. 1.

One of the stator laminations 26 which is stacked together with aplurality of other stator laminations of identical construction to formthe stator core 24 is shown in FIG. 15. The lamination 26 has agenerally central opening 72, and a plurality of stator teeth 74defining slots 76 therebetween opening into the central opening andextending generally radially outwardly from the central opening. Notches78 at the four corners of the lamination 26 define the channel 66 of thestator core 24 (FIG. 3). As shown in FIG. 16, the laminations 26 arestamped from a strip W (from a roll R) of highly magnetically permeablematerial in a die D. All stator laminations 26 are preferably square inshape to permit maximum usage (and correspondingly less waste) of thematerial in the strip W. The slots 76 are shaped and arranged around theperiphery of the central opening 72 so that the arrangement of slots issymmetrical about a pair of perpendicular lines L1 and L2 lyinggenerally in the plane of the stator lamination 26 and intersectinggenerally at the center C of the central opening. The arrangement ofslots 76 is also symmetrical about a diagonal line L3 lying in the planeof the stator lamination 26, passing through the center C of the centralopening 72 and making an angle of 45° with the perpendicular lines L1,L2.

Stated another way, the size and arrangement of slots 76 of the statorlaminations 26 are "90° symmetrical", i.e., any stator laminationsuperposed with another stator lamination may be rotated relative to theother stator lamination 90°, or any multiple thereof, about an axisperpendicular to the plane of the laminations and passing through thecenter C of the laminations, and the slots 76 will be substantiallysuperposed and coextensive. However, it is to be understood that therotational symmetry of the slots 76 could be other than 90° and stillfall within the scope of the present invention. Generally speaking,rotational symmetry of the slots 76 of N°, where N is less than 180,will permit at least incremental improvement in the roundness andstraightness of the stator bore 40.

As is known, the 90° symmetry of the stator laminations 26 permits theconstruction of a stator core 24 having a straighter and more nearlycylindrical bore 40. In the final assembly of the motor 20, the rotor 38and the periphery of the stator core bore 40 should preferably have theminimum possible separation, while permitting free rotation of the rotorin the bore. Deviations of the stator core bore 40 from being straightand cylindrical typically occur because of non-uniform thickness ofindividual stator laminations 26 ("gamma variations"), and ellipticaldeformation of the central openings 72 caused by stress relief in thematerial after punching the central opening. It has been found thatthese errors tend to occur equally along the lines L1, L2 shown in FIG.15. All of the stator laminations 26 have the same original orientationwhen they are stamped from the highly magnetically permeable materialand fed one after another in a forward direction to a stacking station.Rotation of each stator lamination 26 from its original orientation 90°relative to the adjacent stator lamination in the stack forming thestator core 24 results in the aforementioned errors tending to canceleach other out. As shown in FIG. 16, rotation of the stator laminations26 is carried out in a revolving barrel B (the "stacking station") intowhich the stator laminations are received after they are stamped. Priorto each stator lamination being driven into the barrel B. it rotates 90°so that adjacent stator laminations 26 in the stack forming the statorcore 24 are rotated relative to each other 90° from their originalorientations. The stacking and rotating of the stator laminations 26continues until the stack reaches a predetermined height correspondingto the size of the stator core 24.

The four pole start winding 28, four pole run winding 30 and six polerun winding 32 are schematically illustrated on the stator lamination 26shown in FIG. 15. Each winding 27 has a pair of magnet wire leads 80 atopposite ends of the winding which are connected to a source of power asdescribed in detail hereinafter. It is to be understood that the precisearrangement of the windings 27 may be other than shown in FIG. 15 andstill fall within the scope of the present invention. As may be seenfrom the winding diagram, turns of magnet wire from different windingswill lie in the same slots 76.

Difficulty in exploiting the advantage derived from 90° rotation of eachstator lamination 26 arises when the stator core 24 is wound for a twospeed motor of the type disclosed herein having two windings each with adifferent number of poles (e.g., a four pole winding 30 and a six polewinding 32). More specifically, the difficulty occurs when one of thewindings has a rotational symmetry which differs from and is not a wholenumber factor of the rotational symmetry of the stator laminations 26.Rotational symmetry of a winding is equal to the angular spacing of thepoles of the winding around the periphery of the stator core bore 40. Inthe six pole winding 32, the poles are spaced at 60° intervals aroundthe stator core bore 40, and no two poles of the six poles are spacedapart by 90°. If the six pole winding 32 is rotated 90° from an initialposition, its appearance is not the same as it was in the initialposition. Difficulty in winding a 90° symmetric stator occurs generallywhen two of the windings have a different number of poles, and thenumber of one of the poles is an even number which is greater than twoand not a multiple of four.

Accordingly, when the six pole winding 32 and four pole winding 30 (orfour pole start winding 28) are wound on the stator 22, some of theslots 76 adjacent two sides of the lamination will be required toreceive substantially more turns of magnet wire than others. In thepast, accommodation has been made by making the lamination slots whichreceive extra turns of wire deeper. However, this introduces asymmetryin the arrangement of slots, making them no longer 90° symmetric.Moreover, the amount of material to carry the magnetic flux produced bythe windings is reduced along two of the edges of the lamination. Theamount of material along each side of the lamination 26 is referred toas the "yoke" of the lamination. Preferably, the yoke should be nearlythe same along all four edges of the lamination 26. The decrease inmaterial caused by the depth of the slots can be remedied by making thelamination with an elongated rectangular shape. However, theserectangular laminations (not shown) are only symmetrical when rotated180° relative to each other. Less effective cancellation of gammadeviations and elliptical deformations of the central openings 72 occurswith 180° rotation of the stator laminations 26 when forming the statorcore 24.

The stator lamination 26 of the present invention has been constructedto receive magnet wire from the four and six poles windings 28, 30, 32of a two speed motor in a 90° symmetrical arrangement of the slots 76.The yoke along the four peripheral edges of the lamination 26 issubstantially the same, with the minimum distance y separating thebottom of any of the slots 76 and the nearest edge of the statorlamination 26 being approximately equal along all four edges of thelamination. However, a sinusoidal distribution of the turns of magnetwire at each pole of each winding 27 would result in certain slots 76being overfilled and other slots being under-filled. The amount a slot76 is filled with wire is commonly expressed in terms of "slot fillpercentage", which corresponds to a ratio of the cross sectional area ofthe magnet wire times the number of turns in the slot, divided by thearea of the slot. The slot fill percentage of each slot 76 should begreater than about 30% and less than about 70%, and more preferably begreater than about 40% and less than about 60%. To achieve slot fillpercentages in this range in a stator 22 made up of 90° symmetricalstator laminations 26, the spatial distribution of turns of magnet wireamong the slots 76 at least some of the poles of some of the windings isdistorted from an ideal sinusoidal distribution of turns for theparticular number of slots of the stator. More turns of wire are placedin some slots 76 and fewer in others than would be called for in anideal sinusoidal distribution of turns. Further, the distortion of theturns from the sinusoidal distribution is dissimilar at least two of thepoles of one of the windings 27 resulting in the introduction of acontrolled amount of even harmonics upon energizing the winding.Preferably, the distortion should occur in the run winding (i.e., thefour pole winding or six pole winding 32) which is used least inordinary operation of the motor 20. Distortion is carried out so as tobring the slot fill percentages within the preferred ranges. Another,lesser preferred way of bringing slot fill percentages within anacceptable range is to remove turns from one or more of the poles of oneof the windings 27. The precise arrangement of the turns will dependupon the size of the stator 22, the number of windings 27 and poles ineach winding, as well as the desired operating characteristics of themotor 20.

Two preferred winding configurations for the motor of the presentinvention, having a stator 22 with 36 slots wound with a four pole startwinding (designated "4P START"), four pole main winding (designated "4PMAIN") and six pole winding (designated "6P") are diagrammaticallyillustrated in FIG. 21, and compared with a sinusoidal winding andanother winding. The lettered columns represent slots in the stator 22,as indicated on the stator lamination 26 shown in FIG. 15, and the linesbetween the columns represent the teeth 74 of the stator. The numbers inthe columns are the number of turns received in the slot for aparticular winding, and each row of numbers represents the distributionof turns for the winding designated at the right hand side of the row.The rows are arranged in four vertically spaced groups of three rows,each group representing all windings on a given stator. At the bottom ofFIG. 21, the location and span of the coils of each pole for each of thewindings are schematically indicated by nested brackets. The bracketsillustrate generally the possible spans of the coils, but in fact thedesigner may chose not to include one of the spans shown by thebrackets. In winding groups where it has been chosen not to includeparticular spans, the number "0" has been placed in the slots whereturns of wire making up that span would ordinarily be received. Theinstance where a particular slot or slots 76 lie at the interior of thepole, and no wire is placed them, the absence of wire is indicated bydashed lines "- - ".

The top group of windings is a sinusoidal distribution of turns for the36 slot stator 22 illustrated herein. A sinusoidal winding configurationis ordinarily preferred for best motor performance. However, in thisinstance, some of the slots are too full and others relatively empty,making it completely impractical to manufacture. The winding groupsecond from the top in the diagram of FIG. 21 is a first attempt toreduce the disparity in the number of turns received in respective slots76. Although this second winding configuration makes better use of theslots by distorting the turns from the sinusoidal configuration, it isalso impractical to manufacture. The third and fourth groups from thetop are manufacturable winding configurations and are believed tooperate within acceptable parameters.

The completed stator 22 is supported together with the rotor assembly 36in the final assembly of the motor 20 by the first and second end frames50, 52. The rotor 38 is received inside the stator bore 40 and is in aclosely spaced relation with the stator core 24 in the stator core bore.The end frames 50, 52 are each formed from sheet metal blank which isformed into a cup-shaped configuration including generally square, flatinterior and exterior faces (designated 90 and 92, respectively) and askirt 94 projecting outwardly from the interior face 90 of the endframe. Four feet 96 extend laterally outwardly from the outer edges ofthe skirt 94 at the corners of the end frames 50, 52. The centralopening 48 of each end frame is generally tubular in shape, and aninwardly projecting retaining lip 98 narrowing the central opening atits axially outer end is disposed for engaging the bearing (44 or 46)received in the opening. Referring now to FIGS. 4 and 5, material isremoved from the end frames 50, 52 at circumferentially spaced locationsaround their respective central openings 48 leaving vents 100 permittingcirculation of cooling air through the motor. However, not all of thematerial at the location of the vents 100 is removed from the end frames50, 52. At each vent 100, material is left forming a retaining tab 102which extends axially inwardly from the inner end of the central opening48 at the periphery of the opening.

The first bearing 44 includes an inner race 106, an outer race 108 andball bearings 109 received in the races (FIGS. 1 and 3). The inner race106 is fixedly connected to the rotor shaft 42 of the rotor assembly 36adjacent one end, and the shaft and first bearing 44 are located in thecentral opening 48 in the first end frame 50 with the outer race of thefirst bearing engaging the retaining lip 98. The retaining tabs 102 aredeformed inwardly against the outer ring 108 of the first bearing 44 sothat the first bearing is captured in the central opening 48 between theretaining lip 98 and retaining tabs (FIG. 2). Thus, the first end frame50 is positively located relative to the first bearing 44 and the rotor38. The second bearing 46, described in more detail below, and theopposite end of the rotor shaft 42 are located in the central opening 48of the second end frame 52. The second bearing 46 is captured in thecentral opening 48 between the retaining tabs 102 and retaining lip 98of the second end frame 52 in the same way as the first bearing 44 (FIG.5).

The relative radial position of the stator 22 and rotor assembly 36 iscontrolled by the locator nubs 60 and locator holes 62 associated withthe first and second end frames 50, 52 and the stator core 24. The endframes 50, 52 each include four of the locator nubs 60, one on each ofthe four feet 96 of the end frame. As best seen in FIG. 10, each locatornub 60 is received in a corresponding locator hole 62 formed in the endface of the stator core 24, thereby positively radially locating thestator core and the end frames 50, 52. The nubs 60 are preferably formedby punching through the end frames 50, 52 at the feet 96 so that thenubs extend outwardly from the feet a substantial distance into theholes 60 upon assembly of the end frames with the stator 22. Positivelocation of the end frames 50, 52 and stator core 24 also producespositive location of the rotor assembly 36 and stator core 24 by virtueof the first and second bearings 44, 46 being captured in the centralopenings 48 of respective end frames. In the preferred embodiment, thelocator nubs 60 and the central openings 48 of the end frames 50, 52 arepunched from the sheet metal blank during the same stroke of the die,which permits a close tolerance to be maintained on the distance fromthe center of the central openings 48 and the center of the locator nubs60. Likewise, the locator holes 62 in each stator lamination 26 areformed during the same stroke of the press which forms the centralopening 72 of the lamination so that the distance between the center ofthe stator bore 40 formed by the stacked stator laminations 26 and thecenter of the locator holes 62 is maintained within a close tolerance.The maintenance of these close tolerances in turn allows the relativeradial position of the rotor assembly 36 and stator core 24 to bemaintained within a tight range for each motor manufactured.

The locator nubs 60 of the end frames 50, 52 are disposed on anembossment 112 formed on each foot 96 of the end frames and protrudinginwardly from an inwardly facing surface 114 of the foot (FIG. 4). Asshown in FIG. 10, the embossments 112 are the portions of the feet 96 ofeach end frame 50, 52 which engage a respective end face of the statorcore 24. All of the embossments 112 on each end frame 50, 52 are formedat the same time in the die so that their relative location is veryprecise, more so particularly than the relative location of the inwardlyfacing surfaces 114 of the feet 96. The embossments 112 on each endframe 50, 52 are generally located in a plane so that when they engagethe stator core 24 the end frame is not undesirably pitched or cockedwith respect to the stator core. As a direct consequence, thelongitudinal axis of the rotor shaft 42 is better aligned with thecenterline of the stator core bore 40.

Referring now to FIGS. 3 and 11-14, the second bearing 46 includes aplastic, tubular housing formed from first and second pieces (generallyindicated at 116 and 118, respectively) and having a shaft receivingpassage 120. An annular raceway defining member 122 is disposed in theshaft receiving passage 120 and extends around the shaft receivingpassage. A plurality of long, thin needle bearings 124 (broadly, "shaftbearing means") are disposed in the raceway of the raceway definingmember 122 and engage the rotor shaft 42 in the shaft receiving passage120. The rotor shaft 42 is received through the shaft receiving passage120 of the second bearing 46 and is supported for rotation by engagementwith the needle bearings 124, but is free of any fixed connection to thesecond bearing. Thus, the shaft 42 and second bearing 46 are free toslide lengthwise of each other such that the location of the secondbearing on the rotor shaft is determined by the engagement of the secondend frame 52 with the stator core 24.

The first and second pieces 116, 118 of the second bearing housing aresubstantially identical, each having a cylindrical outer wall 126 sizedfor close fitting reception in the central opening 48 of the second endframe 52 and a generally cylindrical inner wall 128 which is concentricwith and spaced radially inwardly of the outer wall. As shown in FIG.13, the outer and inner walls 126, 128 are joined by three generallythin, arcuate diaphragm portions 130 extending between the inner andouter walls. The arcuate diaphragm portions 130 are spaced angularly ofeach other around the shaft receiving passage 120 by arcuate voids 132.The arrangement of arcuate diaphragm portions 130 and voids 132 is suchthat the relative location of diaphragm portions and voids is exactlyreversed about a transverse line L4. Thus, when the second piece 118 isrotated about the line L4 and brought into engagement with the firstpiece 116, the diaphragm portions 130 of the first piece are received inthe voids 132 of the second piece and vice versa. The diaphragm portions130 of the first and second pieces 116, 118 form a continuous annulardiaphragm 134 when the first and second pieces are mated together.

Preassembly of the second bearing 46 is carried out by installing theraceway defining member 122 in the first piece 116 of the housing. Theraceway defining member 122 engages a locating shoulder 136 formed inthe first piece 116 and projects out of the first piece. The secondpiece 118 slides over the exposed portion of the raceway defining member122 and into engagement with the first piece 116. The raceway definingmember engages another locating shoulder 138 in the second piece 118,and the diaphragm portions 130 of the first and second pieces mate inthe way described above to form the continuous diaphragm 134. The firstand second pieces 116, 118 are temporarily held on the raceway definingmember 122 by friction fits, and there is preferably no separateconnection of the pieces to one another. Upon installation of the secondbearing 46 in the central opening 48 of the second end frame 52, andbending of the retaining tabs 102 against the second piece 118, thefirst and second pieces are held together by engagement with theretaining tabs and the retaining lip 98 of the central opening 48. It isto be understood that the second bearing 46 may be formed as one pieceor otherwise than precisely described herein and still fall within thescope of the present invention.

The rotor shaft 42 may extend through the shaft receiving passage 120 ofthe second bearing 46 at an angle to the longitudinal axis L5 of theshaft receiving passage in the undeformed configuration of the secondbearing housing. In that event, the diaphragm 134 deforms by deflectingout of its plane to permit the shaft receiving passage 120 to be pivotedto generally align itself with the longitudinal axis LA of the rotorshaft 42. However, the diaphragm 134 has sufficient strength of resisttranslational movement of the rotor shaft 42 in directions perpendicularto its longitudinal axis LA so that the shaft does not wobble as itrotates in operation. The plastic material of the second bearing housingpieces 116, 118 has a preferred modulus of elasticity in the range of400,000 to 800,000 psi. It is believed that a modulus of elasticity ofthe plastic as high as 2,500,000 would still permit the second bearing46 to function properly. Steel and other materials having far greatermoduli of elasticity could be used if made sufficiently thin.

To reduce noise in operation, the clearance between the needle bearings124 and the rotor shaft 42 is taken up by intentionally canting thesecond bearing 46 relative to the longitudinal axis LA of the rotorshaft 42. Canting is accomplished by an asymmetrical formation (broadly"canting means") on the housing, which in the illustrated embodimentcomprises a pair of longitudinally and radially opposite bumps 140 onthe outer walls 126 of the first and second housing pieces 116, 118 (seeFIGS. 12 and 14). The bump 140 associated with the first housing piece116 engages the retaining lip 98 in the central opening 48 of the secondend frame 52, causing the second bearing 46 to be tilted relative to thesecond end frame in the central opening. As illustrated in FIG. 2, thebump 140 is sized so that the logitudinal axis L5 of the shaft receivingpassage 120 makes an angle of approximately 1° with the longitudinalaxis LA of the rotor shaft 42. The angle shown in FIG. 2 has beengreatly exaggerated for purposes of illustration. The intentionalmisalignment of the axes of the shaft receiving opening 120 and therotor shaft 42 causes the shaft to bear against the needle bearings 124and to elastically deform the diaphragm 134. The elasticity of thediaphragm material provides a reaction force against the rotor shaft 42so that the needle bearings 124 are held against the shaft. Thisconstant, forced engagement of the rotor shaft 42 and the needlebearings 124 significantly reduces noise during operation.

The bump 140 on the second housing piece 118 is not necessary to producethe desired cant of the second bearing 46 relative to the longitudinalaxis of the rotor shaft 42. Of course, the bump 140 is present on thesecond piece 118 because it is identical to the first piece 116. To doaway with the bump 140 on one of the housing pieces would requirecompletely separate molds for the two pieces 116, 118 which isundesirable from the stand-point of cost and simplicity of assembly.However, the bump 140 on the second piece 118 also facilitatesinstallation of the second bearing 46 in the central opening 48 of thesecond end frame 52 with the desired cant. More specifically, the bumpon the second piece is constructed for engagement with an installingtool (not shown) having a flat face which engages the radially inner endof the second piece 118 for pushing the second bearing 46 into thecentral opening 48 of the second end frame 52. The bump 140 on thesecond piece 118 causes the second piece, and hence the entire secondbearing 46 to be canted in the same direction as the engagement of thebump 140 on the first piece 116 with the retaining lip 98. Thus, thedesired misalignment is achieved even when, as will occur from time totime, the bump 140 on the first piece 116 is not fully seated againstthe retaining lip 98 in the central opening 48.

The windings 27 may be connected to a source of electrical power via theplug and terminal assembly 56 mounted on the second end frame 52 of themotor 20. As shown in FIG. 7, the plug and terminal assembly 56 includesa two-piece casing, generally indicated at 150, made of insulatormaterial, and a plurality of lead terminals 152 which receive the magnetwire leads 80 extending from the windings 27. The lead terminals 152each have a serrated formation 154 including a plurality of sharpenedridges so that when the lead terminals 152 are crimped onto the magnetwire leads (as shown for the top terminal in FIG. 7), the insulation ofthe magnet wire is penetrated by the ridges to provide electricalconnection. In the preferred embodiment, the lead terminals 152 areAmplivar® terminals manufactured by Amp, Inc. of Harrisburg, Pa.Referring to FIG. 9, a switch 157 forming part of a switch circuit(generally indicated at 155) housed in the casing 150 is operablebetween a first switch mode (shown in solid lines) in which the startwinding 28 is activated and a second switch mode (shown in phantom) inwhich the start winding is deactivated. The switch 154 is operated bythe centrifugal mechanism 58 in a way which is well known in the art.Generally, the centrifugal mechanism 58 rotates with the rotor shaft 42,and extends as the revolutions of the shaft reach a predetermined levelto actuate a lever arm 159 which opens the switch 157. As shown in FIG.5, a plurality of electrical connectors (designated sequentially byreference numerals 156a-156f) protruding from casing 150 areelectrically connected to lead terminals 152 through the switch circuit.The electrical connectors 156a-156f are constructed as plugs for plug-inconnection to a source of electrical power.

The switch circuit 155 is of conventional construction and isschematically shown in FIG. 9 as part of the electrical circuitincluding the windings 27, a plug 160 from the power source and controlswitches associated with the power source. A pair of leads 162, 164 arerespectively interposed between electrical connectors 156b and 156c anda pair of terminal posts 166, 168 of a single pole double throw speedselector switch 170. Speed selector switch 170 has a movable arm 172 forselective circuit making engagement with its cooperating posts 166, 168,and the switch arm 172 is connected in circuit relation with a lineterminal LT1. A switch 173 located in the circuit between the electricalconnector 156a and the six pole (low speed) winding 32 is shown in itsmotor start position in which the four pole (high speed) winding 30 willbe activated even of the arm 172 of the selector switch 170 has beenmoved to post 168 for low speed operation of the motor 20. The switch173 is moved as a result of actuation of the lever arm 159 by thecentrifugal mechanism 58 to de-energize the four pole winding 30 andenergize the six pole winding 32 when the motor reaches thepredetermined speed. Of course, when high speed (i.e., the four polewinding 30) is selected by moving the arm 172 into engagement with post166, movement of the switch 173 out of electrical contact with the fourpole winding does not result in energization of the six pole winding 32or de-energization of the four pole winding 30.

Another line terminal LT2 is connected by a lead 174 with electricalconnector 156f, the line terminals LT1, LT2 defining the power source. Adouble pole double throw reversing switch 176 of the type well known inthe art is used for controlling the direction of current through startwinding 28 and, consequently, the direction of rotation of the motor 20.A lead 178 connects the reversing switch 176 to a terminal post 166 ofspeed selector switch 170. Other leads, designated 180a-180c, connectthe reversing switch 176 to electric connectors 156d, 156e and 156a,respectively. A ground lead 182 connects the second end frame 52 toground, as described in more detail below.

The casing 150 of the plug and terminal assembly 56 is formed with anintegral stall 186 for receiving a thermal protector indicated generallyat 188 (shown exploded from the stall in FIG. 3) which protects themotor 20 from overloads. The thermal protector 188 has a housing 189 andtwo contacts 190 projecting from it for connection to the switch circuit155. The thermal protector 188 may be inserted into the stall 186 withthe contacts 190 extending further into the casing 150 generally inregistration with contacts 192 of the switch circuit 155 (FIG. 9). Asshown in FIG. 7, two openings 194 on each side of the casing 150 arelocated at the junction of the thermal protector contacts 190 and switchcircuit contacts 192 (not seen in FIG. 7). A joining tool (not shown) isextended through the openings 194 to join (as by soldering) the thermalprotector contacts 190 to the switch circuit contacts 192.

As shown in FIGS. 4 and 5, the plug and terminal assembly 56 issupported in a cutout 200 formed in the skirt 94 of the second end frame52 without fixed connection to the end frame or other part of the motor20. Slot defining formations, generally indicated at 202, on each sideof the plug and terminal casing 150 define slots 204 which receiverespective edge margins 206 of the second end frame 52 bounding thecutout 200. The slots 204 are sized so that the slot defining formations202 grip the second end frame edge margins 206 in the slots tofacilitate holding the plug and terminal assembly 56 in position.However, the slot defining formations 202 do not grip the edge margins206 of the second end frame 52 so tightly as to prevent the plug andterminal assembly 56 from being manually slid into and out of the cutout200. The plug and terminal assembly 56 is further secured in position inthe cutout 200 by locating post means comprising in this embodiment asingle generally triangular locating post 208 generally adjacent one endof the plug and terminal assembly, and a pair of flat end surfaces 210of the slot defining formations 202 located adjacent the opposite end ofthe plug and terminal assembly. The locating post 208 and the flat endsurfaces 210 are formed as one piece with the casing 150. As shown inFIG. 8, the locating post 208 and flat end surfaces 210 engage one endface of the stator core 24 and urge the plug and terminal assembly 56against the second end frame 52 at the closed end of the cutout 200. Acylindrical projection 212 at the axially inner end of the locating post208 is received in one of the slots 76 of the stator. Thus, it may beseen that the plug and terminal assembly 56 is mounted on the motor 20without welding and without any nuts, bolts or other fastening devices.

The first and second end frames 50, 52 of the motor are grounded byconnection to the ground associated with the power source (e.g., theframe of a washing machine) by a ground tab (designated generally byreference numeral 218) formed as one piece with the second end frame. Asshown in FIGS. 4 and 5, the ground tab 218 is located at the bottom ofthe cutout 200 in the second end frame 52. The cutout 200 is formed inthe sheet metal blank at a location correspond-ing to one side of theskirt 94 of the second end frame 52. However, the metal is notcompletely removed and a portion remains as a flap 220 extendinglaterally outwardly from the second end frame 52 at the bottom of thecutout 200. The ground tab 218 is stamped out of the material in theflap 220 and bent to project axially inwardly from the flap. Anelectrical connector portion 222 of the ground tab 218 projects radiallyoutwardly of the remainder of the tab, and a stabilizing finger 224extends axially inwardly of the electrical connector portion.

The plug and terminal assembly casing 150 is formed with an opening 228which receives the ground tab 218 upon insertion of the plug andterminal assembly 56 into the cutout 200. As shown in FIG. 5, theelectrical connector portion 222 of ground tab 218 as received in casing150 is aligned with the other electrical connectors 156a-156f which areadapted to be connected to the plug 160 associated with the power source(FIG. 9). The stabilizing finger 224 is received in a recess 230 at theend of the opening 228 defined in part by an overhang portion 232 of thecasing 150 (FIG. 6). In the recess 230, the stabilizing finger 224 isheld by engagement with the overhang portion 232 and the portion of thecasing 150 opposite the overhang portion from substantial movementtransverse to the lengthwise extension of the finger as shown in FIG. 6.Thus, the stabilizing finger 224 aids in holding the plug and terminalassembly 56 in place in the cutout 200 in the second end frame 52 byresisting tilting movement of the plug and terminal assembly casing 150.

Referring now to FIGS. 17-19, the rotor assembly 36 of the presentinvention is made up of a stack of generally thin, circular rotorlaminations 240 made of highly magnetically permeable material. Slots242 in the rotor laminations 240 are spaced circumferentially around theperiphery of the rotor laminations. As shown in FIG. 19, each slot 242includes a radially inner portion 244 and a radially outer skew portion246 extending outwardly and laterally (e.g., circumferentially), fromthe radially inner portion toward the circumference of the rotorlamination 240. The radially inner portion 244 of each slot 242 at leastpartially overlies corresponding radially inner portions of slots on theother rotor laminations in the stack forming the rotor 38. The overlyingslots 242 define axially extending passages in which rotor bars 248 aredisposed. The rotor bars 248 are formed by pouring molten aluminum oranother suitable conductor into the passages formed by the overlyingslots (FIG. 17). However, it is to be understood that rotor bars may beplaced in the rotor 38 by other methods, such as press fitting, andstill fall within the scope of the present invention. The rotor bars 248are not shown in FIGS. 18 and 19 for clarity, but are connected at theends thereof by end rings (not shown) to form a squirrel cage rotorconductor arrangement as will be understood by persons skilled in theart.

The rotor laminations 240 in the stack defining the rotor 28 arearranged in three adjacent sets, designated 250, 252 and 254,respectively. The slots 242 in the first set of laminations 250 havetheir skew portions 246 extending laterally in a first direction, theslots in the second set of laminations 252 have their skew portionsextending laterally in a second direction opposite the first, and theslots in the third set of laminations 254 have their skew portionsextending laterally in the first direction. All of the rotor laminations240 are virtually identical. Thus, the slots 242 are of substantiallythe same size and shape, and thus the slots in the second set oflaminations 252 (as arranged in the stack) appear to be mirror images ofthe slots in the first set 250 and third set 254 of laminations. Asshown in FIG. 19, the radially inner portions 244 of partially overlyingslots of the first set 250 and second set 252 of laminations generallyoverlie each other. However, the skew portions 246 of the first set 250and second set 252 of laminations have no portions which are overlying.The skewed condition of the skew portions 246 of the slots 242 of thesecond set 252 of laminations relative to the skew portions of the firstset 250 and third set 254 of laminations facilitates decoupling from therotor bars 248 of stator slot order winding harmonics and stator slotopening permeance harmonics. The first set 250 and third set 254 ofrotor laminations have slots 242 which are oriented the same way, andthe second set of laminations 252 is interposed between the first andthird sets. The dimension of each of the first set 250 and third set 254of rotor laminations parallel to the longitudinal axis LA of the rotorshaft 42 is preferably approximately equal to 1/4 the total axialdimension of the rotor, and the dimension of the second set oflaminations 252 is preferably approximately equal to 1/2 the total axialdimension of the rotor. The arrangement of the sets 250, 252, 254 ofrotor laminations produces a more balanced rotor which reducesmechanical noise in operation of the motor 20. Moreover, the arrangementof laminations 240 into the three sets 250, 252 and 254 reduces currentloss due to leakage from the rotor bars into the laminations 240. It isto be understood that the rotor 38 may be formed from two sets of rotorlaminations 240 having slots 242 which are skewed, or more than threesets of rotor laminations and still fall within the scope of the presentinvention. The skew of the present design is easily manufactured andprovides particularly good performance for single phase motors.

Referring to FIGS. 17 and 19, the laterally outermost points L of theskew portions 246 of the overlying slots 242 in said first set of rotorlaminations 250 lie generally along a first axially extending line A1and the laterally outermost points of said skew portions of thecorresponding slots in said second set of rotor laminations 252 liegenerally along a second axially extending line A2. The skew of theslots 242 in the first and second sets may be represented by thedistance d between the first line A1 and the second line A2. In thepreferred embodiment, the distance d falls within a range expressed bythe following equation,

    (2πr)/(2S-P)<d≦(2πr)/(2S-P)+δ+ρ     (1)

The variable r is the radial distance between the center of the rotorlamination 240 and the either line A1 or A2 (FIG. 18). S is the numberof slots in the stator core, and P is the number of poles of a selectedone of the windings (the harmonics of which are to be decoupled from therotor). As explained in more detail below, ρ/2 corresponds to thedistance between the laterally outermost point L of the slot 242 and itsradially outermost point R (FIG. 19), and δ/2 generally corresponds tothe distance δ/2 between a first magnetic saturation region M1 and asecond magnetic saturation region M2 (FIG. 20).

More specifically, ρ/2 is the distance between first and second parallelplanes (which are seen on edge in FIG. 19 and appear as lines A3 and A4,respectively) in a third plane (which is also seen on edge in FIG. 19and appears as line A5) which includes the lines A1 and A2. The firstplane A3 includes the radially outermost point R of the skew portion 246of the slot, and the second plane A4 includes the line A1 or A2. Thefirst plane A3 and second plane A4 intersect the third plane AS at rightangles, and all three planes (A3, A4, A5) are perpendicular to the planein which FIG. 19 lies.

The distance δ/2 is explained with reference to FIG. 20 showing two setsof rotor laminations 258 having slots 260 with skew portions 246 whichextend laterally in opposite directions. The illustrated skewed slots260 do not have the same shape as the slots 242 shown in FIG. 19.Generally, the rotor laminations 240 having slots 242 have more materialbetween the slot and the circumference of the rotor lamination 240 thanthe rotor laminations 258 having slots 260. The configuration of theslots 260 is an initial configuration chosen on the assumption that, foreach slot 260, the sole location of magnetic saturation is region M1adjacent the radially outermost point R of each slot which correspondsto the slot bridge (i.e., the narrowest strip of material surroundingthe slot). However, as explained below, we have found and unexpectedresult that a second saturation region M2 occurs at a location spacedfrom the first saturation region M1. The distance δ/2 corresponds to thedistance between parallel lines, designated A6 and A7, respectively.Line A6 is perpendicular to the plane A5 and intersects the firstsaturation region M1 (and radially outermost point R). Line A7 is alsoperpendicular to plane A5 and intersects the second saturation regionM2.

The stator slot order harmonics which are decoupled by the skew of therotor bars 248 are represented by:

    n=2mS/P±1                                               (2)

where n is the harmonic order number, m is the mode number (typicallym=1), S is the number of slots in the stator core 24, and P is thefundamental number of magnetic poles of the motor 20. In order todecouple a particular stator slot order harmonic, the mutual reactance Xof the slot should go to zero. Mutual reactance X may be expressed bythe following equation for the skew geometry of the rotor bars 248 ofrotors embodying the present invention:

    X=X.sub.m X.sub.α, where X.sub.α =cos (nα/4)(3)

X.sub.α is the component of mutual reactance attributable to the angle αof skew of the rotor bar in "electrical" degrees. In order to decouple aparticular harmonic X.sub.αn :

    αn/4=π/2                                          (4)

Substituting for n in equation (2), the angle of skew α needed todecouple the stator slot order harmonics can be expressed as:

    α/2=π(2S/P±1)                                  (5)

The conversion to mechanical degrees of skew is made by substitutingα=α_(mech) P/2, or:

    α.sub.mech /2=2π/(2S±P)                        (6)

Thus, the predicted distance d' in plane A5 between the lines A1 and A2,defined above, may be found by substituting for α_(mech) in equation(6):

    α.sub.mech =2πd'/(2πr)                         (7)

or, after simplification:

    d'=(2πr)/(2S±P)                                      (8)

It is apparent from equation (7) that distance d' is the length of anarcuate segment of a circle having a radius r. The arcuate segmentcorresponding to d' would be defined by the intersection of radial lines(not shown) passing through the laterally outermost points L of the skewportions 246 with the circle of radius r. However, the differencebetween the linear distance between end points of the arcuate segment oflength d' and the length d' is so small that it has been represented asa linear distance in the drawings. Likewise, the distances δ and ρ,which are actually lengths of arcuate segments of a circle having aradius r, are shown for simplicity as linear distances in a plane A5.The distances δ/2 and ρ/2 are large relative to the difference betweenthe arcuate distance and the linear distance between end points of thecorresponding arcuate segments. The arcuate segment of length δ/2 wouldbe defined by the intersection of radial lines (not shown) passingthrough the first and second saturation regions M1 and M2, respectively,with the circle of radius r. The arcuate segment of length ρ/2 would bedefined by the intersection of radial lines (not shown) passing throughthe radially outermost point R and laterally outermost point L of a slot242 with the circle of radius r.

The predicted distance d' (which is actually a range due to the presenceof ±P) does not in fact equate to the distance d between laterallyoutermost points of the skew portions 246 of the slots 242 of the rotorlaminations of the first set 250 and second set 252. The predicteddistance d' must be first corrected by adding ρ/2 for both the slots ofthe first set 250 of rotor laminations and the slots of the second set252 of rotor laminations to account for the distance (ρ/2) in the planeline A5 between the radially outermost point R and the laterallyoutermost point L intersecting line A1 of the first set slot, and thedistance (ρ/2) in the plane A5 between the radially outermost point Rand the laterally outermost point L intersecting line A2 of the secondset slot. Ideally, ρ would equal zero and the radially outermost point Rwould coincide with the laterally outermost point L. However, the slot242 should preferably have a finite radius of curvature at the radiallyoutermost point R to accommodate manufacture so the two points L and Rdo not actually coincide.

However, even when the distance d' has been modified to account for thenoncoincidence of the radially outermost point R and the laterallyoutermost point L, the optimum skewing for single phase motors has notbeen acheieved. The equations (3)-(8), used to predict the necessaryskew distance d', clearly assume that the location of magnetic fluxsaturation (M1) will be in the narrowest strip of rotor laminationmaterial between the slot 260 and the outer circumference of thelamination 258 (i.e., generally at the radially outermost point R of theslot). Referring to FIG. 20, the predicted distance between laterallyoutermost points L of the slots 260 having oppositely extending skewportions is d'+ρ. In FIG. 20, ρ/2 is the distance between a first plane(seen on edge in FIG. 20 and represented by line A6) and a second plane(also seen on edge in FIG. 20 and represented by line A8). The firstplane A6 intersects the radially outermost point R and is perpendicularto a third plane seen on edge in FIG. 20 and represented by line A5. Thesecond plane A9 is parallel to the first plane A6 and intersects a lineincluding the laterally outermost points L of the axially aligned slotsof a respective set of rotor laminations 258.

However, we have surprisingly found that for single phase motors thereis a second saturation region M2 spaced from the first region M1, asdiscussed above (FIG. 20). In order to compensate for this unexpectedanomaly, the skew distance d is further increased from the predicteddistance d'+ρ by δ, where δ/2 corresponds to the distance between thenarrow strip (i.e., first magnetic saturation region M1) and the secondsaturation region M2, as stated above. The skew distance d will alwaysbe greater than the predicted distance d'. Accordingly, the lower limitfor the skew distance d will be greater than the upper predicteddistance d' (i.e., d>πD/(2S-P)+ρ). The amount δ varies from slotto-slotand with the rotational position of the rotor 38 relative to the stator22. Therefore, δ is actually an averaged value of the actual δassociated with each slot 242. Presently, we have determined δ bothexperimentally, and by use of a finite element analysis of the rotor 38.In view of the foregoing, d would preferably be chosen as:

    d=πD/2S+ρ+δ                                   (9)

where the quantity ρ+δ is sufficiently large so that the distance dstill exceeds the predicted distance d', or:

    ρ+δ>πD/(2S-P)-πD/(2S)                      (10)

The dynamoelectric machine (induction motor 20) of the present inventionis constructed for ease, speed and precision of assembly. The componentparts of the motor shown in FIG. 3 may be assembled without the used offasteners other than the keys 64. Nut and bolt fasteners may becompletely eliminated. As discussed above, many of the component parts,in particular the stator 22 and the end frames 50, 52, have beenconstructed to achieve greater precision and to facilitate the finalassembly of the motor 20. The following is an example of one way inwhich the motor components shown in FIG. 3 might be assembled together.However, this example is not exclusive of other possible methods ofassembly, particularly in the order of assembly.

The first bearing 44 is press fit onto the rotor shaft 42 of the rotorassembly 36 at a predetermined location. The centrifugal mechanism 58 isfixed to the rotor shaft 42 on the opposite side of the rotor 38 fromthe first bearing 44. The end of the rotor shaft 42 mounting the firstbearing 44 is inserted into the central opening 48 of the first endframe 50 with the first bearing engaging the retaining lip 98 of thecentral opening to terminate further movement of the rotor shaft andfirst bearing through the opening. The retaining tabs 102 are bent overagainst the first bearing 44 to capture the first bearing in the centralopening 48 of the first end frame 50.

The stator 22 is placed over the rotor assembly 36 with the rotor 38being received in the stator core bore 40. One end face of the statorcore 24 engages the embossments 112 on the feet 96 of the first endframe 50, and the locator nubs 60 are received in corresponding locatorholes 62 of the stator core 24. The stator windings 27 are connected tothe plug and terminal assembly 56 by placing the magnet wire leads 80into respective lead terminals 152 and crimping the terminals againstthe magnet wire (FIG. 7). The ridges of the serrated formation 154 ofthe lead terminals 152 penetrate the magnet wire insulation and bringthe lead terminals into electrical connection with the magnet wires.

The second bearing 46, assembled as previously described, is secured inthe central opening 48 of the second end frame 52 by bending over theretaining tabs 102 against the bearing. The second end frame 52 isplaced over the end of the rotor shaft 42 opposite the first end frame50 and the rotor shaft is received in the shaft receiving passage 120 ofthe second bearing 46. The plug and terminal assembly 56 is mounted onthe second end frame 52 by pushing it into the cutout 200. The slots 204of the slot defining formations 202 have flared mouths 234 at one end tofacilitate entry of the edge margins 206 bordering the cutout 200 intothe slots (FIGS. 4 and 5). The ground tab 218 is received into theopening 228 in the casing 150 as the plug and terminal assembly 56 ispushed into the cutout 200, and the stabilizing finger 224 enters therecess 230. The electrical connector portion 222 of the ground tab 218is aligned with the electrical connectors 156a-156f of the plug andterminal assembly 56 so that it is prepared to be plugged into theground lead 182 when the motor 20 is connected to a source of electricalpower.

The second end frame 52 is pushed toward the end face of the stator core24 with the rotor shaft 42 sliding through the shaft receiving passage120 until the embossments 112 on the feet 96 of the second end frame 52engage the end face of the stator core with the locator nubs 60 receivedin the locator holes 62 in the stator core. The motor components aresecured together by placing the keys 64 into the channels 66 in thestator core 24 and deforming the ends 68 of the keys over onto the feet96 of respective end frames 50, 52. The intentional misalignment of theaxis L5 of the shaft receiving passage 120 of the second bearing 46 withthe longitudinal axis LA of the rotor shaft 42 causes the diaphragm 134of the second bearing to be elastically deformed and hold the needlebearings 124 against the rotor shaft.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. A dynamoelectric machine comprising:a statorincluding a stator core having a pair of opposing end faces, a borethrough the stator core extending from one end face to the other endface, windings including a start winding and at least one run winding onthe stator core, each winding having winding leads extending outwardlyfrom the stator; first and second opposite end frames mounted onrespective end faces of the stator core, each end frame having agenerally central opening therein; bearing means associated with thecentral openings of the first and second end frames; a rotor assemblycomprising a shaft received in said bearing means, and a rotor fixedlymounted on the shaft for conjoint rotation therewith, the rotor beingdisposed at least in part in the stator core bore, the rotor and thestator being adapted for magnetic coupling upon activation of thewindings for rotating the shaft and rotor relative to the stator and endframes; a plug and terminal assembly including a casing made of aninsulator material, a plurality of lead terminals electrically connectedto the winding leads and a plurality of electrical connectors protrudingfrom the casing and electrically connected to the lead terminals, theelectrical connectors being constructed for connecting the winding leadsto a source of electrical power, and a ground tab formed as one pieceout of the material of the second end frame, the around tab including anelectrical connector portion; the casing having an opening thereinreceiving the ground tab with the electrical connector portion of theground tab disposed adjacent to at least one of the electricalconnectors for plug-in electrical connection to a ground remote from thedynamoelectric machine upon connection of the electrical connectors tosaid source of electrical power.
 2. A dynamoelectric machine as setforth in claim 1 wherein the ground tab further comprises a fingerprojecting outwardly from the ground tab, and wherein the plug andterminal assembly casing has a recess therein receiving the finger, thefinger being adapted to engage the casing in the recess to facilitatestabilization of the plug and terminal assembly on the second end frame.3. A dynamoelectric machine as set forth in claim 2 wherein the plug andterminal assembly comprises means engaging the second end frame forsupporting the plug and terminal assembly on the second end frame, saidplug and terminal assembly being free of fixed connection to the secondend frame.
 4. A dynamoelectric machine as set forth in claim 3 whereinsaid supporting means comprises slot means receiving an edge margin ofthe second end frame therein, the plug and terminal assembly beingsupported on the second end frame by engagement with the plug andterminal assembly in said slot means.
 5. A dynamoelectric machine as setforth in claim 4 wherein said slot means comprises two slot-definingformations formed as one piece with the casing, each slot-definingformation having a slot therein receiving a corresponding edge margin ofthe second end frame.
 6. A dynamoelectric machine as set forth in claim5 wherein the second end frame includes a cutout in which the plug andterminal assembly is located with opposite lateral edge margins of thesecond end frame bordering the cutout being received in correspondingslots of the slot-defining formations, and wherein the ground tab islocated generally at the closed end of the cutout.
 7. A dynamoelectricmachine as set forth in claim 6 wherein the second end frame is stampedfrom sheet metal blank, and wherein the ground tab is formed from sheetmetal material remaining after the cutout is cut into the sheet metalblank.
 8. A dynamoelectric machine as set forth in claim 3 wherein theplug and terminal assembly further comprises a locating post projectingfrom the casing and into engagement with the stator core for holding theplug and terminal assembly in a positive location on the first end framewhereby the plug and terminal assembly is secured to the dynamoelectricmachine without the use of fasteners.
 9. A dynamoelectric machine as setforth in claim 1 wherein the plug and terminal assembly furthercomprises a switch housed in the casing operable between a first switchmode in which the start winding is activated and a second switch mode inwhich the start winding is deactivated, the lead terminals beingintegrally and directly connected to the switch at the housing andreceiving the winding leads of the windings thereby providing directconnection of the windings to the switch.
 10. A dynamoelectric machineas set forth in claim 1 wherein the lead terminals each comprise meansfor penetrating the magnet wire insulation, said penetrating means beingin electric contact with the magnet wire.
 11. A dynamoelectric machineas set forth in claim 10 wherein said penetrating means comprises aserrated formation formed integrally with each lead terminal.
 12. Adynamoelectric machine as set forth in claim 9 wherein the thermalprotector comprises a housing, a thermally activated switching mechanismlocated in the housing, and contacts electrically connected to theswitching mechanism and protruding from the housing at one end thereof,the contacts being electrically connected to the switch at saidlocations in the plug and terminal assembly casing.
 13. A dynamoelectricmachine as set forth in claim 9 wherein the casing comprises a stallformed as one piece with the casing and receiving the thermal protectortherein, the thermal protector being electrically connected to thewindings by attachment to the switch at locations in the casing, thecasing having openings therein in registration with respective locationsof attachment of the thermal protector to the switch.
 14. Adynamoelectric machine comprising:a stator including a stator corehaving a pair of opposing end faces, a bore through the stator coreextending from one of the end faces to another of the end faces,windings including a start winding and at least one run winding on thestator core; first and second opposite end frames mounted on respectiveend faces of the stator core, each end frame having a generally centralopening therein; bearing means generally disposed in the centralopenings of the first and second end frames; a rotor assembly comprisinga shaft received in said bearing means, and a rotor fixedly mounted onthe shaft for conjoint rotation therewith, the rotor being disposed atleast in part in the stator core bore, the rotor and the stator beingadapted for magnetic coupling upon activation of the windings forrotating the shaft and rotor relative to the stator and end frames; saidbearing means comprising first and second bearings, the first bearingbeing disposed in the central opening of the first end frame and fixedlymounted on the rotor shaft thereby to prevent axial movement of therotor shaft relative to the first bearing, the second bearing beingdisposed in the central opening of the second end frame, the secondbearing comprising a housing and shaft bearing means supported by thehousing in a shaft receiving passage, said shaft bearing means beingconstructed and arranged for rolling engagement with the rotor shaft insaid shaft receiving passage for supporting the rotor shaft andpermitting rotation of the rotor shaft about its longitudinal axis, saidshaft bearing means being free of connection to the rotor shaft; thesecond bearing further comprising cant means engageable with the secondend frame for canting the longitudinal axis of the shaft receivingpassage relative to the longitudinal axis of the rotor shaft whereby theshaft bears against said shaft bearing means and elastically deforms thehousing.
 15. A dynamoelectric machine as set forth in claim 14 whereinthe longitudinal axis of the shaft receiving passage makes an angle ofapproximately 1° with respect to the longitudinal axis of the rotorshaft.
 16. A dynamoelectric machine as set forth in claim 14 whereinsaid cant means comprises an asymmetrical formation on the housing ofsaid second bearing means.
 17. A dynamoelectric machine as set forth inclaim 16 wherein said asymmetrical formation comprises at least one bumpformed as one piece with the housing of said second bearing means, thebump engaging the second end frame in the central opening thereof.
 18. Adynamoelectric machine as set forth in claim 16 wherein saidasymmetrical formation comprises two bumps formed as one piece with thehousing of said second bearing means, the bumps being disposed ongenerally longitudinally opposite ends of the housing and on generallyopposite sides of the longitudinal axis of the shaft receiving passageof said second bearing means, a first of the bumps being engageable withthe second end frame in the central opening thereof, and a second of thebumps being adapted for engagement with an installing tool forfacilitating installment of said second bearing means at an angle cantedto the longitudinal axis of the rotor shaft.
 19. A dynamoelectricmachine as set forth in claim 14 wherein the second bearing furthercomprises an interior raceway extending generally around the shaftreceiving passage, and wherein said shaft bearing means comprises aplurality of needle bearings disposed in the raceway, the needlebearings engaging the rotor shaft in the shaft receiving passage.
 20. Adynamoelectric machine as set forth in claim 14 wherein the housing ofthe second bearing is formed from an elastic material such that thehousing is operable to resiliently deform to permit the rotor shaft toextend through the shaft receiving passage of the housing at an angle tothe longitudinal axis of the shaft receiving passage in an undeformedconfiguration of the housing while maintaining rolling engagement of theneedle bearings with the rotor shaft.
 21. A dynamoelectric machine asset forth in claim 20 wherein said elastic material is a polymericmaterial.
 22. A dynamoelectric machine as set forth in claim 21 whereinthe housing is constructed to prohibit translational movement of therotor shaft in directions perpendicular to the longitudinal axis of therotor shaft.
 23. A dynamoelectric machine as set forth in claim 22wherein the housing of the second bearing comprises a generally tubularouter wall sized for reception in the central opening of the second endframe, and a substantially concentric tubular inner wall spaced radiallyinwardly of the outer wall, and a generally thin, annular diaphragmextending between and joining the inner and outer walls, the diaphragmbeing constructed for deflection to permit the rotor shaft to extendthrough the shaft receiving passage of the second bearing at an angle tothe longitudinal axis of the shaft receiving passage in the undeformedconfiguration of the housing.
 24. A dynamoelectric machine as set forthin claim 20 wherein the housing of the second bearing comprises agenerally tubular outer wall sized for reception in the central openingof the second end frame, a substantially concentric tubular inner wallspaced radially inwardly of the outer wall, and a generally thin,annular diaphragm extending between and joining the inner and outerwalls, the diaphragm being constructed to permit the rotor shaft toextend through the shaft receiving passage of the second bearing at anangle to the longitudinal axis of the shaft receiving passage in theundeformed configuration of the housing.
 25. A dynamoelectric machinecomprising:a stator including a stator core having a pair of opposingend faces and wire-receiving slots, a bore through the stator coreextending from one of the end faces to another of the end faces, and atleast one winding on the stator core formed by magnet wire received inthe slots on the stator core; first and second opposite end framesmounted on respective end faces of the stator core, each end framehaving a generally cup-shaped configuration including interior andexterior faces, a skirt projecting outwardly from the interior face anda generally central opening through the interior and exterior faces, thesecond end frame having a cutout in the skirt bounded by edge margins;bearing means associated with the central openings of the first andsecond end frames; a rotor assembly comprising a shaft received in saidbearing means, and a rotor fixedly mounted on the shaft for conjointrotation therewith, the rotor being disposed at least in part in thestator core bore, the rotor and the stator being adapted for magneticcoupling upon activation of the winding for rotating the shaft and rotorrelative to the stator and end frames; a plug and terminal assemblyincluding a casing made of an insulator material, lead terminalselectrically connected to the winding and electrical connectorsprotruding from the casing and electrically connected to the leadterminals, the electrical connectors being constructed for connectingthe winding leads to a source of electrical power, the plug and terminalassembly casing having slot means receiving at least one of the edgemargins of the second end frame bounding the cutout therein whereby theplug and terminal assembly is supported on the dynamoelectric machinefree of any fixed connection to the second end frame or stator; saidslot means comprising two slot-defining formations formed as one piecewith the casing, each slot-defining formation having a slot thereinreceiving a corresponding one of the edge margins of the second endframe, the slot-defining formations each being constructed to define aflared mouth portion of the slot adapted to facilitate installation ofthe plug and terminal assembly in the cutout.
 26. A dynamoelectricmachine as set forth in claim 25 wherein the plug and terminal assemblyfurther comprises a locating post projecting from the casing and intoengagement with the stator core for holding the plug and terminalassembly in a positive location on the second end frame.
 27. Adynamoelectric machine as set forth in claim 26 wherein a distal end ofthe locating post is received in one of the slots of the stator core.28. A dynamoelectric machine as set forth in claim 27 wherein thelocating post comprises a cylindrical projection at the distal end sizedfor reception in said one stator core slot.
 29. A dynamoelectric machineas set forth in claim 25 further comprising a ground tab directlyengaging and in electrical connection with the second end frame, andwherein the casing of the plug and terminal assembly has an openingtherein receiving the ground tab with the ground tab being disposed forelectrical connection to ground upon connection of the electricalconnectors of the plug and terminal assembly to ground.
 30. Adynamoelectric machine as set forth in claim 29 wherein the ground tabis formed as one piece with the second end frame.
 31. A dynamoelectricmachine as set forth in claim 30 wherein the ground tab includes anelectrical connector portion located generally adjacent the electricalconnectors of the terminals and constructed for plug-in connection to aground remote from the dynamoelectric machine.
 32. A dynamoelectricmachine as set forth in claim 31 wherein the ground tab furthercomprises a finger projecting outwardly from the ground tab, and whereinthe plug and terminal assembly casing has a recess therein receiving thefinger, the finger being adapted to engage the casing in the recess tofacilitate stabilization of the plug and terminal assembly on the secondend frame.
 33. A dynamoelectric machine as set forth in claim 30 whereinthe second end frame is stamped from a sheet metal blank, the ground tabbeing formed from sheet metal material remaining after the cutout is cutinto the sheet metal blank.